1. Field of the Invention
The present invention generally relates to a thin film transistor and, more particularly, to a thin film transistor having an active layer being multi-layered.
2. Description of the Related Art
Due to the progression of the semiconductor technology, thin film transistors are developed as electrical switches, and are widely used in electrical equipments. As an example of flat panel displays, the thin film transistor is used as a switch that controls the charging or discharging operations of the storage capacitor used in controlling the pixels.
A conventional thin film transistor has an active layer generally made of a single-layered metal oxide. One example of this conventional thin film transistor can be seen in the paper entitled “Room-temperature fabrication of transistors using amorphous oxide semiconductors” as published by Keniji Nomura, Hiromichi Ohta, Akihiro Takagi, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono in Nature, Vol. 432.
In the conventional thin film transistor, the amorphous/poly silicon of the active layer is replaced by InGaZnO (IGZO) in order to improve the utility of the metal oxide in flat pane displays. However, during the use of the conventional thin film transistor, the carriers cannot be concentrated when flowing in the active layer, resulting in a low carrier mobility.
In light of the above, it is necessary to improve the conventional thin film transistor for improved utility.